The present invention relates to heavy-duty friction clutches of the type used for large automotive vehicles such as trucks, tractor-trailers, and the like and, more particularly, to a torque-limiting clutch brake assembly.
The use and function of a clutch brake are well known in the art, as discussed, for example, by Flowtow et al. (U.S. Pat. No. 4,762,215) and Babcock (U.S. Pat. No. 4,512,450). A clutch brake is a device used to facilitate shifting by retarding the rotation of transmission gears when the clutch is disengaged by the vehicle operator. Typically, a clutch brake is a disk-shaped device which is splined to the gearbox input or drive shaft of a transmission and is activated by a throw-out mechanism when the clutch is disengaged. The spinning clutch brake is thereby sandwiched between the throw-out mechanism and gearbox housing, creating a frictional drag or braking effect to slow the input shaft.
In normal use, a clutch brake wears out and must be replaced, which usually requires lowering and disassembling the vehicle transmission--a time consuming and expensive procedure. However, Babcock (U.S. Pat. No. 4,512,450) discloses a design in which the clutch brake splits into halves so that it can be replaced without extensive disassembly of the transmission. This greatly reduces the cost of replacement.
Torque-limiting designs take a different approach. They reduce the frequency of replacement necessary by improving clutch brake longevity. They accomplish this by permitting the clutch brake to slip when excessive braking pressure is applied, thereby avoiding the excessive stresses which contribute to wear and tear. Also, unlike traditional designs, a torque-limiting clutch brake will not disrupt vehicle operation when improperly applied. Torque-limiting clutch brakes, such as Flowtow et al. (U.S. Pat. No. 4,762,215), have heretofore used a friction coupling between an outer housing and inner collar member. When the torsional force between the housing and collar is too great, they slip relative to each other and thereby avoid damage.
While such torque-limiting designs work relatively well for their intended purpose, the clutch brake still eventually fails and must be replaced. However, prior art torque-limiting clutch brake designs do not split into halves and so must be replaced by lowering and disassembling the clutch and transmission. Furthermore, the components used in prior art friction type torque-limiting mechanisms must be of constant dimension and have no discontinuities in order to maintain a constant slip torque. Therefore, these designs can not readily be made in splittable sections because such sections inherently have discontinuities.
Accordingly, it is a principle object of the present invention to provide a torque-limiting clutch brake which can be removed and installed without disassembling the transmission.
More particularly, it is an object to provide a torque-limiting clutch brake which can be split into halves and put back together.
A related object is to provide an improved torque-limiting mechanism which facilitates such a split design.